The mineralization of calcium phosphate phases will be studied under highly reproducible conditions by the addition of well- characterized seed material to stable supersaturated solutions of calcium phosphate both at physiological pH and at pH levels typical of those leading to the formation of carious lesions. Reactions will be followed by monitoring the ionic concentrations in the supersaturated solutions and by studying the solid phases formed using x-ray diffraction, specific surface area, optical and electron microscopy. In addition, dissolution kinetic experiments will be used to determine the nature of the surface phases formed at various stages of the crystallization reactions. Studies will be made with synthetic calcium phosphate preparations, enamel, the inorganic and organic components of dentine and with predentine as seed material. The effects of ions such as magnesium, stannous and fluoride and of caries inhibitors will be investigated. The characterization of the intermediate calcium phosphate phases will provide much more detailed information than has hitherto been available concerning the ways in which the additives modify the course of the mineralization reaction. Studies will also be made under conditions simulating those for plaque and calculus formation.